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Tal 100r Tal diagonal change options.


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Hi

I have seen a thread on The Tal 100r that states that the Tal diagonal can't be changed for  another due to it being chamfered which others aren't.

I would like to know if any one has seen or overcome this issue.

As always many thanks.

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Well maybe time to end this thread, as no one appears to have found a solution, I will have a go myself, will post again one way or the other.

Trevor 

 

 

 

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Hi,

I have just had a look at the diagonal from my 100r and it isn’t chamfered, it is however quite small although I don’t have another 1.25” diagonal to compare or to see if it would fit ok.


Im almost certain even with my Meade shorty 2x Barlow there isn’t enough inward travel to achieve focus.

hope that helps, Doug.

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2 hours ago, DougM43 said:

Hi,

I have just had a look at the diagonal from my 100r and it isn’t chamfered, it is however quite small although I don’t have another 1.25” diagonal to compare or to see if it would fit ok.


Im almost certain even with my Meade shorty 2x Barlow there isn’t enough inward travel to achieve focus.

hope that helps, Doug.

any chance you could post a pic of it Doug?

I guess the barlow won't then fit direct into the focuser tube either?

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There you go,

I have never thought to put a Barlow straight into the focus tube, it’s not a super snug fit but not to slack either and may just work, 

3621C778-460F-4581-B784-062BC8315D5F.jpeg

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92400B57-5BB4-497A-AC4E-8E38DC187AB0.jpeg

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Posted (edited)

ahh I see now, so that tapered collar is for the locking screws to hold it in place when you loosen them to rotate the diagonal I expect. The rest of the nose is likely 1.25-inch (or might even be the russian 32mm std) but of course the collar with the thumbscrews on the focuser tube prevents a regular 1.25-inch unit being inserted far enough and maybe then affects the focus range (lack of in-focus).

Makes me wonder tho if that black collar can't be unscrewed from the focuser drawtube? 

Would give more inward movement but you'd then need to find a way to lock the regular diagonal/eyepiece in place.

Edited by DaveL59
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I don’t think the black collar comes off, not easily anyway (I just tried) 

if you were really desperate to use a Barlow then the simplest way I would think would be to unscrew the whole back focus part from the tube, cut an inch or so off the tube length and re fix the back part back on, it would need to be measured carefully though or you may find you end up without enough outward focus travel.

I think the later 100rs has a shorter tube length as well as a longer focus tube to overcome the problems reported with the 100r.

 

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Posted (edited)
19 minutes ago, DougM43 said:

I don’t think the black collar comes off, not easily anyway (I just tried) 

if you were really desperate to use a Barlow then the simplest way I would think would be to unscrew the whole back focus part from the tube, cut an inch or so off the tube length and re fix the back part back on, it would need to be measured carefully though or you may find you end up without enough outward focus travel.

I think the later 100rs has a shorter tube length as well as a longer focus tube to overcome the problems reported with the 100r.

 

It's actually Trevor that's asking as he's just bought a 100R, I'm just adding thoughts as I already have the 100RS with 2-inch R&P focuser so no issues, as you said shorter OTA and long focuser drawtube. That flanged design is also on their 100RS 2 to 1.25 inch adaptor as I recall as on that I can ease off the lock screw and rotate the diagonal with no risk it drops out. Clever design, simple engineering solution.

Agreed tho, shorten the OTA and refit the focuser then if you need more outward focus use an extension tube to make up for the lost length. Just a case of being able to make it secure, fabricate a flanged collar perhaps to fit onto a regular 1.25-inch barrel. Or perhaps a parfocal ring a couple mm away from the base of the nosepiece to give the locking screws something similar to grip against.

Edited by DaveL59
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You should be able to just fit longer screws to clamp a regular 1.25” diagonal nose piece and the Tal 2x barlow has a chamfered nose to fit the diagonal without hitting the glass i think. It’s very good optical quality if a little warm perhaps

Mark

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Hello Doug

As always thanks for responding

That does help me understand the problems I will face.

In all good conscience I can't see me bringing my self to cut the back off. I can see that it  would work, it will be interesting to see if my Tal 3x Barlow comes into focus. What is surprising is that on other threads people have mentioned using non Tal Barlow's successfully, will have a word with other astronomy club members to see if I can borrow one to try.

I would also like to know if you have ever collimated the scope either by shimming the main objective or adjusting the mirror on the diagonal, or as other threads mention both?

As always many thanks for your assistance. 

Trevor

 

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Hello Dave 

As always many thanks for responding.

I can now start to understand the issue. Looking at the diagonal main body it does look slightly shorter on one side, which if unique would allow it to go further in, am I correct in this?

The other thought is about diagonal construction, would it be possible to remove the chamfered part and place it on another diagonal?

And finally have you any thoughts about collimating a Tal refractor, is it necessary, would I still use the Cheshire, and how do you go about it?

As always thanks for your assistance.

Regards

Trevor

 

 

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Posted (edited)
39 minutes ago, Trevor PC said:

Hello Dave 

As always many thanks for responding.

I can now start to understand the issue. Looking at the diagonal main body it does look slightly shorter on one side, which if unique would allow it to go further in, am I correct in this?

The other thought is about diagonal construction, would it be possible to remove the chamfered part and place it on another diagonal?

And finally have you any thoughts about collimating a Tal refractor, is it necessary, would I still use the Cheshire, and how do you go about it?

As always thanks for your assistance.

Regards

Trevor

 

 

 

Not having seen one in real life I can't say if the chamfered part would unscrew nor if the thread would match another diagonal body, so something you could try when you get it in your hands maybe. I expect that collar is used in part to pull the diagonal tight and square into the focuser tube and part to allow easy rotation of the diagonal when adjusting for the angle of the scope on an EQ mount. Simply slacken the locking screws a little, turn and re-tighten. No risk the diagonal drops out onto the ground 🙂

I would say tho, do be careful tightening the screws and don't use too much force else you can strip the threads in the metal body. The one that holds the finder on mine I found had part stripped and the finder wouldn't hold securely. I had to drill and re-tap a size up to sort it so I now use nylon thumbscrews to avoid a repeat.

 

For collimating, there you have 2 units to consider as it happens. The OTA itself you would adjust the focuser and/or objective lens so that it is all concentric around the focuser drawtube and the focuser is square vs the objective lenses. The objective lens cell has set screws at the edge that are used to tweak the lens for alignment so shouldn't need any shims. A laser would likely be the most useful for that as the other Dave showed in his fettling thread where he replaced his focuser, but hopefully won't need doing.

The other unit is the diagonal and that has small set screws in the back for adjusting the mirror tilt, again no shims needed.

I haven't had to adjust either on my 100RS so can't guide but there may be other long-time members here who have and can advise better if you find you need to. 

Mark is right in that longer thumbscrews could be used to hold a regular 1.25-inch fitting, but that wouldn't overcome the lost 5mm or so that the black outer collar takes up and may also introduce some tilt, but until you try you won't find out for sure. A parfocal ring on the nosepiece might address tilt tho as it'd act similar to that chamfered collar on the TAL diagonal. A prism diagonal may do enough to cover that lost distance, may not.

Has me wondering now too, do the TAL metal bodied barlows fit into that focuser collar when inserted into the scope?
Then I guess the diagonal into the barlow and away you go?

Edited by DaveL59
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10 hours ago, DaveL59 said:

It's actually Trevor that's asking as he's just bought a 100R, I'm just adding thoughts as I already have the 100RS with 2-inch R&P focuser so no issues, as you said shorter OTA and long focuser drawtube. That flanged design is also on their 100RS 2 to 1.25 inch adaptor as I recall as on that I can ease off the lock screw and rotate the diagonal with no risk it drops out. Clever design, simple engineering solution.

Agreed tho, shorten the OTA and refit the focuser then if you need more outward focus use an extension tube to make up for the lost length. Just a case of being able to make it secure, fabricate a flanged collar perhaps to fit onto a regular 1.25-inch barrel. Or perhaps a parfocal ring a couple mm away from the base of the nosepiece to give the locking screws something similar to grip against.

Dave did you fit the 2" R&P focuser if so could you please pm me how you did it as I would like to do that with mine. 

Cheers 

Paul 

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4 minutes ago, wookie1965 said:

Dave did you fit the 2" R&P focuser if so could you please pm me how you did it as I would like to do that with mine. 

Cheers 

Paul 

Hi Paul, no my 100RS came with that focuser fitted, as per pic it's held with screws around the collar where it fits over the main tube.

image.thumb.png.e640a47689d16c700cc5b01a129e1076.png

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Here's what I mean re the 2-1.25 inch adaptor on the 100RS 2-inch R&P focuser. It is also made with that chamfer but the drawtube doesn't have any step like the early 100R R&P does. My thinking as said earlier - it helps nip the unit in square to the drawtube and also means just slacking the thumbscrews a touch allows you to turn the diagonal without risk it'd plummet to the ground, neat engineering IMHO.

image.png.49097d33a3ddd058dc18e655f62c0eb2.png

 

The white plastic thing is a 35mm film cannister drilled out at the end and has a silica gel sachet inside - a DIY desiccant cap 🙂 

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58 minutes ago, DaveL59 said:

Hi Paul, no my 100RS came with that focuser fitted, as per pic it's held with screws around the collar where it fits over the main tube.

image.thumb.png.e640a47689d16c700cc5b01a129e1076.png

Right that looks like the original R&P I thought you have fitted a different one. I fitted a skywatcher dual focuser to my Meade 127mm. I have fitted a bigger focuser wheel to the TAL to aid fine focus. 

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20220705_102416.jpg

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Hello Dave

As always many thanks for responding.

I did start to pen a response to you a little time ago about attaching a diagonal to the Tal Barlow, but didn't because it looked like it would not have  enough inward travel, but will give it a go.

Will  invest in a laser if need be, and make a paper mask to cover the primary.

Here's hoping that it gets to me from Scotland  in the next month or so without any problems.

As an avid reader of threads, it looks like the Tal 100r had  an aluminium OTA where the RS was steel,  how this effects the positioning and sealling of baffles I am unsure.

As always many thanks for your assistance

Trevor

 

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Posted (edited)
56 minutes ago, Trevor PC said:

Hello Dave

As always many thanks for responding.

I did start to pen a response to you a little time ago about attaching a diagonal to the Tal Barlow, but didn't because it looked like it would not have  enough inward travel, but will give it a go.

Will  invest in a laser if need be, and make a paper mask to cover the primary.

Here's hoping that it gets to me from Scotland  in the next month or so without any problems.

As an avid reader of threads, it looks like the Tal 100r had  an aluminium OTA where the RS was steel,  how this effects the positioning and sealling of baffles I am unsure.

As always many thanks for your assistance

Trevor

 

I had thought they were ally too, but a magnet does stick to the OTA on my 100RS so I'd say steel it is. The other TAL reflectors I have are all ally tho.

No idea if the idea of barlow-diagonal-eyepiece would work but worth a go. Bear in mind tho that it'll increase mag to more than the rated barlow because of the extra distance from the barlow lens. How much I don't know but your x3 may become more like x5 which could be too much for the optics.

For the baffles I did find a thread on here for converting to solar (PST) and that showed the removed baffles, which were likely a push-in fit.

So pulling the baffles and then using flocking to improve them and the inner OTA tube might be feasible.

 

Edited by DaveL59
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Posted (edited)
54 minutes ago, wookie1965 said:

Right that looks like the original R&P I thought you have fitted a different one. I fitted a skywatcher dual focuser to my Meade 127mm. I have fitted a bigger focuser wheel to the TAL to aid fine focus. 

20220705_102450.jpg

20220705_102416.jpg

Hi Paul

nah I find the OEM R&P works just fine so no need to change it. You can probably tell too from other posts I like to keep things reasonably original tho like you I did also fit one larger focusing knob to aid fine focusing 🙂 Yet to seriously look at how best to mount one of the Tasco motor focusers to it but then I don't find it wobbles that much when focusing compared to the SW130 or Celestron LT70 starsense scopes.

Another Dave has swapped his focuser out and made up a collar to suit

 

 

 

Edited by DaveL59
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4 hours ago, DaveL59 said:

Hi Paul

nah I find the OEM R&P works just fine so no need to change it. You can probably tell too from other posts I like to keep things reasonably original tho like you I did also fit one larger focusing knob to aid fine focusing 🙂 Yet to seriously look at how best to mount one of the Tasco motor focusers to it but then I don't find it wobbles that much when focusing compared to the SW130 or Celestron LT70 starsense scopes.

Another Dave has swapped his focuser out and made up a collar to suit

 

 

 

Thank you for replying and posting the link looks really interesting. I use a 2" diagonal on my 100rs had a bit of trouble with higher mag eyepieces so I got a different 2-1.25mm adapter. 

https://www.firstlightoptics.com/adapters/baader-low-profile-eyepiece-adapter-for-steeltrack.html

Had no problem since. 

Paul 

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Hello Dave

As always thanks for responding.

I hadn't thought about the distance making the magnification greater, so thanks for that.

I would be interested to know how far you have tried pushing the magnification on the RS, and at what point the views lost contrast and sharpness on one of of those rare very clear nights with low  atmosphere turbulence?

The reason for the question is I have seen some threads where individuals are talking up to 300x which is a lot more then I thought possible.

As always many thanks for your assistance.

Trevor 

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Hi Trevor

I probably haven't gone above around x160 with mine but I guess some may have pushed to much higher just to see if it can. Expect the image to darken and soften if you do but never know till you try, seeing permitted of course.

On my little TAL-M 80mm reflector I've gone to x139 and even accidentally didn't take the finder out of the optical path and wondered what I was seeing. That tiny optical finder gave surprisingly good performance with the 15mm and barlow, no idea the mag but not what I'd expected from a 25mm objective lens. I have pushed that scope to I think x189 and things did go a bit soft , no surprise there.

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Hello Wookie 

As always  thanks for responding.

At x333 was the view of still sharp with good contrast?

As always many thanks for your assistance.

Trevor 

 

 

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